Polishing apparatus

ABSTRACT

A polishing head assembly; containing a rotatable spindle, collet and abrasive member; is mounted on a machine frame for both vertical and horizontal movement. The polishing head is moved horizontally in a lowered position to engage a workpiece and polish edges of an aperture where it intersects with a nonplanar surface of the workpiece. In a raised position, the polishing head is engaged by a release mechanism releasing the abrasive member which is fed a predetermined distance outwardly of the polishing head and is engaged by a unit dressing and shaping the abrasive as required for subsequent polishing operations.

United States Patent Happy Oct. 14, 1975 POLISHING APPARATUS Prima Examiner-Donald G. Kell 751x111 dl-la w' ,Mh. Y 1 or aymon 10 Attorney, Agent, or Firm-Charles R. Engle [73] Assignee: General Motors Corporation,

Detroit, Mich. 57] ABSTRACT [22] Filed: Nov. 7, 1974 A polishing head assembly; containing a rotatable spindle, collet and abrasive member; is mounted on a [2n App! 52l783 machine frame for both vertical and horizontal movement. The polishing head is moved horizontally in a [52] [1.8. CI 51/5 D; 51/ 165.87; 51 168 lowered po ition to engage a workpiece and polish [51] Int. Cl. B24B 19/00; B24B 53/04 edges f n per ure where it intersects with a non- [58] Field of Search 51/5 D, 34 D, 31, 71, 16537, planar surface of the workpiece. In a raised position, 51/168, 166 MH, 166 T5 the polishing head is engaged by a release mechanism releasing the abrasive member which is fed a predeter- [56] References Cit d mined distance outwardly of the polishing head and is UNITED STATES PATENTS engaged by a unit dressing and shaping the abrasive as 3 430 388 3/1969 Gabriel 5 1/5 D X required for subsequent polishing operations. 3:634:978 1 1972 Uhtenwoldt 51/5 D x 3 Claim, 4 Drawing Figures U.S. Patent 0m. 14, 1975 Sheet 1 on 3,911,624

US. Patent 0a. 14, 1975 Sheet 2 of2 3,911,624

Fig. 3

I36 I38 I40 I22 30 I28 80 I24I I26 06 I20 I34 I32 D Fig. 4

POLISHING APPARATUS This invention relates to a polishing apparatus and more specifically to such an apparatus having particular application for polishing aperture edges at an area of intersection with a non-planar wall surface.

The polishing of aperture edges on irregular surfaces or non-planar walls frequently presents the problem of positively advancing a polishing tool into engagement with the surfaces in a limited space defined by the particular workpiece. In particular, it is difficult to polish the edges of spark plug apertures in the trochoidal surfaces of rotary engine housings on a mass production basis.

The subject invention provides a polishing apparatus capable of performing these operations by utilizing a polishing head assembly movable between lowered and raised positions on a machine frame and by advancing the polishing head toward the workpiece when in the lowered position in a predetermined relationship with a fixed rotary engine housing. In the lowered position, the polishing head is advanced toward the workpiece surface by a feed cylinder until a cylindrical abrasive member secured in the polishing head engages the spark plug aperture and polishes the edges thereof while rotating against the surfaces a predetermined period of time. The polishing head is then retracted to a predetermined position on the machine frame and is raised vertically to an abrasive feeding and dressing position. In this position, actuating means release the cylindrical abrasive member within the collet and spindle ofthe polishing head assembly while a second actuating means is activated to advance the abrasive member a predetermined distance. In a modification of my invention, a single actuating means is used to both release the abrasive member within the colletand spindle assembly and subsequently advance the cylindrical abrasive member outwardly of the spindle a predetermined distance. After advancement of the cylindrical abrasive member, a dresser unit is actuated to move against the extended portion of the abrasive member and grind the tip portion to a desired configuration so that the shape of the abrasive member is the same during each polishing operation thereby specifically engaging the aperture edges as required to polish the edges.

A general object of my invention is the provision of a polishing apparatus relatively simply constructed and economically operated for the precise engagement of aperture edges in a non-planar surface and including means advancing an abrasive member in the polishing apparatus as well as maintaining a desired shape of the abrasive member prior to each polishing operation.

Another object of my invention is the provision of a polishing apparatus including a machine frame, a polishing head assembly vertically and horizontally movable upon the'machine frame for engagement with a workpiece in a vertically lowered position where it is advanced horizontally engaging an abrasive member with and polishing the workpiece while when moved to a vertically raised position the abrasive member is released, fed a predetermined distance outwardly of the polishing head and the end portion of the abrasive member is dressed to a predetermined configuration prior to the next polishing operation.

A further object of my invention is the provision of a polishing head assembly including a spindle rotatably mounted in the polishing head housing and having a collet affixed and positioned therein for rotation with the spindle, the collet including a slanted serrated portion engaging a cylindrical abrasive member permitting movement of the abrasive member in one direction for extension out of the collet and the polishing head, a nose piece secured to the spindle and also including a slanted serrated portion engaging an end portion of the abrasive member retaining it within the spindle, actuating means engaging the collet and moving it axially forward toward the spindle nose piece into engagement therewith extending the abrasive member a predetermined distance out of the polishing head, and spring means biasing the collet rearwardly relative to the spindle when the actuating means is retracted engaging tapered surfaces on the spindle and the collet causing the collet serrated portion to engage the abrasive member and fixedly retain it within the polishing head.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, may be best understood by reference to the following description taken in conjunction with the accompanying drawings in which:

FIG. 1 is an elevational view illustrating the polishing head of my invention in a vertically raised abrasive feeding and dressing position on a machine frame.

FIG. 2 is an elevational view illustrating the polishing head of my invention in a vertically lowered working position with the polishing head shown in phantom advanced to a working position in engagement with a workpiece.

FIG. 3 is a side elevational view partly in section of one form of the polishing head of my invention.

FIG. 4 is an elevational view partly in section of a modified form of the polishing head of my invention.

With reference now to FIG. 1, a machine tool frame 10 includes vertical ways 12 permitting raising and lowering of a polishing head assembly 14 relative to the frame 10. The polishing head 14 is movable upon the ways 12 by a hydraulic positioning cylinder 16 through the extension of actuating rod 18. The machine frame 10 has a collet release hydraulically actuated cylinder 20 affixed thereon adjacent a similar hydraulic cylinder 22 operable to advance an abrasive member 24 in the polishing head 14 as will later be described. A dresser assembly 26 can either be mounted on the machine frame 10 or on a plate adjacent thereto so that a rotary grinding tool 28 can be advanced by a fluid actuated feed cylinder 30 permitting the grinding tool 28 to dress abrasive member 24 to a predetermined configuration. The abrasive member 24 is extended by cylinder 22 until it engages a stop 32 mounted on a dresser assembly frame member 34. The tool 28 is selectively rotated by a conventional motor 36 including a fluid actuated motor schematically shown in FIG. 1.

Referring now to FIG. 2, the polishing head 14 assembly is shown in a vertically lowered working position such that the abrasive member 24 is aligned with an angularly disposed aperture 38 in a workpiece 40. The polishing head 14 is advanced by a feed cylinder 42 engaging the abrasive member 24 with the aperture 38 as shown in phantom wherein the polishing head is in the position generally indicated at 44. Movement of the polishing head 14 by the feed cylinder 42 is accomplished by providing mating horizontal ways 46 on the polishing head and the frame member 10. In a specific application of my polishing apparatus, the workpiece is the center member of a rotary engine housing defining a trochoidal cavity and the aperture 38 is a spark plug aperture specifically positioned in the housing member.

As illustrated in FIG. 3, one form of my invention in cludes a polishing head assembly 14 having a housing 48 rotatably supporting a spindle member 50 upon axially spaced bearing assemblies 52 and 54 retained within cavities 56 and 58 of the housing. The bearing cavities 56 and 58 are formed in axially spaced web portions 60 and 62 of the housing 48, the web portions cooperatively defining a cavity 64 within the housing. A housing end plate 66 is secured to the housing member 48 by a plurality of machine screws 68 and contains an aperture 70 rotatably receiving an enlarged portion 72 of the spindle 50. The bearings 52 and 54 engage the exterior surface of the spindle 50 and are retained in spaced relation by sleeves 74 and 76 which cooperate with a spindle driven gear 78 drivingly connected with spindle 50 via a key 80. A nut 82 threaded upon spindle 50 retains the bearing 52 and sleeve 74 upon the spindle. A lock washer 84 retains the nut 82 in place. The spindle 50 terminates in end portion 86 engaging a seal 87.

A collet 88, which can be formed having a plurality of inherently biased spring fingers 89, is concentrically positioned within the spindle 50 and has an enlarged nut 90 forming an abutment threaded on its rearward end 92. A Belleville spring 94 is placed between the nut 90 and the rearward end 86 of spindle 50 continuously biasing the collet 88 rearwardly within the polishing head housing 48. The biasing of Belleville spring 94 moves collet 88 rearwardly until tapered surface 96 of the collet engages with a mating tapered surface 98 on an internal periphery of spindle 50.

A modified form of my polishing head is illustrated in FIG. 4 wherein like parts are given like reference numerals. In this arrangement, the housing 48 is slightly modified such that a seal 100 is retained in the web 62 adjacent a modified end plate 66. The end plate 66 also contains a seal 102 adjacent aperture 104 receiving a nosepiece 106 secured to spindle 108 by a plurality of machine screws 110. The bearings 52 and 54 are retained within the housing 48 adjacent web portions 60 and 62 by a nut 112 threaded on the rearward end of spindle 108. The bearings are axially spaced by sleeves 74 and 76 placed upon spindle 108. Nosepiece 106 includes a plurality of slanted serrations 114 which are continuously biased into engagement with abrasive member 24 by the inherent spring characteristics of the material forming a plurality of fingers 116 defined by a plurality of axially extending slots 118 in the nosepiece 106. A collet 120 is concentrically positioned within the spindle 108 and is threadedly connected to a pusher bushing 122 at its rearward end. The collet 120 is also split axially to provide a plurality of fingers 124, each having a plurality of slanted serrations 126 adjacent the forward end of the collet 120. The serrations 126 are continuously biased into engagement with the outer surface of abrasive member 24 by the inherent spring characteristics of the material forming collet 120. The pusher bushing 122 cooperates with an abutment 128 on the internal surface of spindle 108 forming a space receiving a coil spring 130 therebetween which continuously urges the collet 120 rearwardly within the polishing head housing 48. The spring 130 is effective to move the collet 120 rearwardly until a tapered surface 132 on the collet engages a mating surface 134 on the internal periphery of the spindle 108 forcing the collet serration 126 into the abrasive member 24 locking it in place. The spindle 108 contains an axially extending slot 136 receiving a drive pin 138, press fit in an aperture 140 in the collett 108, the pin engaging the slot providing a rotary driving connection between spindle 108 and collet 120.

The pusher bushing 122 terminates in a section 142 of a reduced diameter which extends through a seal assembly 144 positioned in an aperture 146 in a rear housing plate 148 retained by a plurality of machine screws 150. The housing web portion 60 also contains a seal assembly 100 sealing the rear plate 148 to the polishing head housing 48.

When the polishing head assembly 14 is in the raised position on frame 10, a collet release and abrasive positioning hydraulic cylinder 150 is positioned rearwardly of the pusher bushing 122. The cylinder 150 includes a pusher plate 152 mounted upon actuating rod 154. The spring 130 normally biases the collet 120 and engages the tapered surfaces 132 and 134 such that a predetermined distance D is provided between the forward end of collet 120 and the rearward surface of nosepiece 106 for a purpose later to be described.

In operation, using the polishing head described in FIG. 3, the polishing head 14 is moved to the vertically raised position by positioning cylinder 16 and hydraulic collet release cylinder 20 is actuated engaging rod 21 with abutment nut 90 moving the collet 88 against the force of Belleville spring 94 thereby disengaging the tapered surfaces 96 and 98 of the collet and spindle respectively. This permits the resilient fingers 89, when formed on collet 88, via their inherent spring characteristics to release from the abrasive member 24. The hydraulic cylinder 22 is then actuated engaging rod 23 with abrasive member 24 and extending it until it engages the stop 32. In this manner the abrasive member is projected a predetermined distance exteriorly of the collet 88 and consequently a predetermined distance exteriorly of the polishing head 14.

Cylinder 22 then retracts rod 23 and cylinder 20 retracts rod 21. The Belleville spring 94 is then again effective moving collet 88 rearwardly in spindle 50 reengaging tapered surfaces 96 and 98 forcing the collet fingers 89 radially inwardly into tight frictional contact with abrasive member 24. In this manner, the abrasive member 24 is tightly positioned within the polishing head and the force of spring 94 is also sufficient to tightly engage the tapered surfaces 96 and 98 establishing a frictional rotary drive connection between spindle 50 and collet 88 for driving the collet with the driven gear 78.

Subsequent to the positioning of abrasive member 24 within the polishing head 14, dresser assembly 26 is actuated extending feed cylinder 30 which moves a base member 33 upon a frame 34 positioning grinding tool 28 adjacent the end portion of abrasive member 24. When the tool 28 is positioned in contact with the abrasive member 24 the fluid or electric rotary motor 36 is energized rotating tool 28 dressing the end of abrasive 24. Upon completion of the dressing cycle the base member 33 is retracted by the feed cylinder 30 moving grinding tool 28 out of engagement with the abrasive member.

The polishing head assembly 14 is then moved to a vertically lowered position on frame via the vertical ways 12 positioning the polishing head 14 as shown in FIG. 2. The polishing head is then advanced by feed cylinder 42 moving the abrasive member 24 into engagement with spark plug aperture 38 in rotary engine frame member 40. The polishing head 14 moves on the horizontal ways 46 which are a part of the polishing head frame member 48. The abrasive member 24 is then rotated a predetermined period of time sufficient to polish the edges of aperture 38. The abrasive member 24 can be and is preferably composed of a flexible abrasive material permitting positive engagement between the abrasive member and the edges of the aperture for removing any rough surfaces around the aper ture. The polishing head 14 is retracted by cylinder 42 to its original position illustrated in FIG. 2 and then is moved to a vertically raised position as illustrated in FIG. 1 for subsequent extension and dressing of the abrasive member.

The operation of the polishing head assembly illustrated in FIG. 4 is similar to that above described except that a single release cylinder 150 is utilized to release collet 120 from spindle 108 and also simultaneously extend abrasive member.24 a predetermined distance. This is accomplished through engagement of pusher flange 152 against bushing 122 actuating the collet 120 against the force of the coil spring 130. Forward movement of collet 120 results in serrations 126 continuing to bite into abrasive member 24 and extend it outwardly of nosepiece 106 as the abrasive member 24 slides past its serrations l 14. The serrations 1 14 and 126 are slanted in a direction so that they act as a oneway clutch permitting extended movement of the abrasive member 24 in a forward direction while preventing retraction of the abrasive member rearwardly within the polishing head 14. The teeth of the serrations are spring biased into engagement with the outer surface of the abrasive via the inherent spring characteristics of the material of fingers 116 and 124 of the nosepiece and collet respectively. The nosepiece 106 and collet 120 are precisely positioned within polishing head frame member 48 providing a predetermined distance D between the forward end of the collet and the rearward end of the nosepiece 106 as shown in FIG. 4. Consequently, forward movement of the abrasive member 24 in response to extension of rod 154 in the cylinder 150 is continued until the space D is closed at which time the collet engages the nosepiece 106. In this manner, the abrasive is extended a predetermined amount regulated by the distance D.

Retraction of rod 154 and pusher flange 152 by the cylinder 150 permits the coil spring 130 to move collet 120 and pusherbushing 122 rearwardly within spindle 108 until tapered surfaces 132 and 134 frictionally engage and force fingers 124 radially inwardly bitingly engaging the serrations 126 with the outer surface of abrasive member 24. This engagement in conjunction with similar biting engagement of serrations 114 on spring fingers 116 positively locks the abrasive member 24 in the predetermined extended position.

The positive locking engagement of the abrasive member 24 by spring fingers 116 of nosepiece 106 and serrations 126 on spring fingers 124 of collet 120 in conjunction with the pin and slot connection 136 and 138 between the collet 120 and spindle 108 provide a driving connection for positive rotation of the abrasive member 24 when driven gear 78 is driven by gear 79 connected with a power source not shown.

While I have shown and described particular embodiments of my invention, it will, of course be understood that various modifications and alternative constructions thereof may be made without departing from the true spirit andscope of my invention and that I intend by the appended claims to cover all such modifications and alternative constructions as fall within the true spirit and scope of my invention.

What is claimed is:

1. An apparatus for polishing intersecting aperture and wall surfaces including a frame movably supporting a rotating polishing head for independent movement both in vertical and horizontal directions, said polishing head comprising a housing, a spindle rotatably mounted in said housing, a collet positioned within said spindle for rotation therewith, an elongated abrasive member adjustably retained within said collet, mating surfaces on said spindle and said collet engaging and retaining said abrasive member in an adjusted position within said collet, spring means normally biasing said surfaces into engagement for retaining said collet within said spindle, collet release actuating means positioned on said frame at a predetermined location, positioning means on said frame moving said polishing head between working and abrasive adjusting positions, said collet being aligned with said collet release means when said polishing head is at the abrasive adjusting position, said collet release means being selectively actuated to move said collet against the force of said spring means extending said abrasive member out of'said collet a predetermined distance compensating for wear of said abrasive member, means for feeding said polishing head toward a workpiece when said head is at the working position, a driven gear drivingly connected to said spindle, and power means drivingly engaging said gear rotating said abrasive member polishing intersecting aperture and wall surfaces when said abrasive member is advanced into engagement with aworkpiece.

2. An apparatus for polishing aperture edges on a workpiece where an aperture intersects with a nonplanar surface, the apparatus including: a frame; a rotating polishing head movable vertically between a lowered polishing position and a raised abrasive feeding and dressing position; said polishing head also being movable horizontally when in the lowered polishing position for advancement into engagement with the nonplanar workpiece surface; said polishing head comprising a housing; a cylindrical spindle; bearing means rotatably supporting said spindle within said housing; a collet positioned within said spindle; means drivingly connecting said collet to said spindle for rotation therewith; a cylindrical abrasive member adjustably retained within said collet and having an end portion extending forwardly of said polishing head from one end of said collet and said spindle, said end portion extending outwardly of said housing for polishing the workpiece aperture edges; a tapered surface on the internal peripheral surface of said spindle adjacent said abrasive member end portion; a tapered surface mating with said spindle tapered surface on the exterior of said collet adjacent said abrasive member end portion; slanted internal serrations on the forward end of said collet; a pusher bushing threaded on one end of said collet and extending rearwardly of said polishing head exteriorly of said housing in a direction axially opposite from said abrasive end portion; an abutment formed on the interior surface of said spindle; a coil spring positioned between said pusher bushing and said abutment biasing said collet rearwardly in said polishing head engaging said tapered surfaces forcing said slanted collet serrations into said abrasive member looking it within said collet; said spindle including a nosepiece having slanted internal serrations engaging the end-portion of: said abrasive member; said nosepiece having an inherent spring characteristic engaging said serrations with abrasive member such that both the collet serrations and the nosepiece serrations permit adjustment of said abrasive forwardly while preventing rearward movement thereof within said collet; an adjusting surface on said spindle positioned a predetermined axial distance away from the forward end of said collet; actuating means operably engaging said pusher bushing for selectively moving said abrasive member and said collet forwardly until said collet forward end and said adjusting surface engage extending the abrasive a predetermined distance out of said polishing head; said nosepiece serrations engaging the abrasive retaining it fixed while said collet is retracted by said coil spring until said tapered surfaces re-engage locking said collet serrations with said abrasive upon disengagement of said actuating means; a dresser unit mounted on said frame; means actuating said dresser unit moving it into engagement with said abrasive end portion while the polishing head is in the raised position dressing the abrasive as required between polishing operations; means advancing said polishing head toward and engaging said abrasive end portion with a workpiece while said polishing head is in the lowered position; a driven gear drivingly connected to said spindle; and power means drivingly engaging said gear rotating said abrasive member polishing the workpiece aperture edges while ishing head also being movable horizontally when in the lowered polishing position for advancement into engagement with'a surface of the curved rotary engine housing at the point it is intersected by the spark plug aperutre; said polishing head comprising a housing; a cylindrical spindle; a bearing assembly adjacent each end of said spindle rotatably supporting it within said housing; a collet positioned within said spindle; a cylindrical abrasive member adjustably retained within said collet with an end portion extending outwardly from a forward end of said collet and said spindle for polishing the rotary engine housing; a tapered surface on the internal periphery of said spindle adjacent said abrasive member end portion; a tapered surface on the exterior of said collet adjacent said abrasive member end portion; an abutment on the rearward end of said collet; a spring between said abutment and the rearward end of said spindle biasing the tapered surface on said collet into engagement with the tapered surface of said spindle squeezing said collet against said abrasive member retaining it in a position with said end portion extended; the biasing force of said spring also being sufficient to frictionally engage said collet and said spindle tapered surfaces providing a driving connection therebetween rotating said collet with said spindle; first actuating means selectively engageable with said abutment moving said collet against the force of said spring and disengaging said tapered surfaces releasing said collet from said abrasive member; second actuating means selectively engageable with said abrasive member and movable a predetermined distance for extending said end portion out of said collet a predetermined working distance; a dresser unit mounted on said frame; means actuating said dresser unit moving it into engagement with said end portion of said abrasive member while the polishing head is in the raised position dressing the working end of said abrasive member as required between polishing' operations; third actuating means advancing said polishing head toward and engaging said abrasive member end portion with said engine housing spark plug aperture while said polishing head is in the lowered polishing position; a driven gear drivingly connected to said spindle; and power means drivingly engaging said gear rotating said abrasive member polishing the spark plug aperture edges while said abrasive is engaged with the rotary engine housing. 

1. An apparatus for polishing intersecting aperture and wall surfaces including a frame movably supporting a rotating polishing head for independent movement both in vertical and horizontal directions, said polishing head comprising a housing, a spindle rotatably mounted in said housing, a collet positioned within said spindle for rotation therewith, an elongated abrasive member adjustably retained within said collet, mating surfaces on said spindle and said collet engaging and retaining said abrasive member in an adjusted position within said collet, spring means normally biasing said surfaces into engagement for retaining said collet within said spindle, collet release actuating means positioned on said frame at a predetermined location, positioning means on said frame moving said polishing head between working and abrasive adjusting positions, said collet being aligned with said collet release means when said polishing head is at the abrasive adjusting position, said collet release means being selectively actuated to move said collet against the force of said spring means extending said abrasive member out of said collet a predetermined distance compensating for wear of said abrasive member, means for feeding said polishing head toward a workpiece when said head is at the working position, a driven gear drivingly connected to said spindle, and power means drivingly engaging said gear rotating said abrasive member polishing intersecting aperture and wall surfaces when said abrasive member is advanced into engagement with a workpiece.
 2. An apparatus for polishing aperture edges on a workpiece where an aperture intersects with a non-planar surface, the apparatus including: a frame; a rotating polishing head movable vertically between a lowered polishing position and a raised abrasive feeding and dressing position; said polishing head also being movable horizontally when in the lowered polishing position for advancement into engagement with the non-planar workpiece surface; said polishing head comprising a housing; a cylindrical spindle; bearing means rotatably supporting said spindle within said housing; a collet positioned within said spindle; means drivingly connecting said collet to said spindle for rotation therewith; a cylindrical abrasive member adjustably retained within said collet and having an end portion extending forwardly of said polishing head from one end of said collet and said spindle, said end portion extending outwardly of said housing for polishing the workpiece aperture edges; a tapered surface on the internal peripheral surface of said spindle adjacent said abrasive member end portion; a tapered surface mating with said spindle tapered surface on the exterior of said collet adjacent said abrasive member end portion; slanted internal serrations on the forward end of said collet; a pusher bushing threaded on one end of said collet and extending rearwardly of said polishing head exteriorly of said housing in a direction axially opposite from said abrasive end portion; an abutment formed on the interior surface of said spindle; a coil spring positioned between said pusher bushing and said abutment biasing said collet rearwardly in said polishing head engaging said tapered surfaces forcing said slanted collet serrations into said abrasive member locking it within said collet; said spindle including a nosepiece having slanted internal serrations engaging the end portion of said abrasive member; said nosepiece having an inherent spring characteristic engaging said serrations with abrasive member such that both the collet serrations and the nosepiece serrations permit adjustment of said abrasive forwardly while preventing rearward movement thereof within said collet; an adjusting surface on said spindle positioned a predetermined axial distance away from the forward end of said collet; actuating means operably engaging said pusher bushing for selectively moving said abrasive member and said collet forwardly until said collet forward end and said adjusting surface engage extending the abrasive a predetermined distance out of said polishing head; said nosepiece serrations engaging the abrasive retaining it fixed while said collet is retracted by said coil spring until said tapered surfaces re-engage locking said collet serrations with said abrasive upon disengagement of said actuating means; a dresser unit mounted on said frame; means actuating said dresser unit moving it into engagement with said abrasive end portion while the polishing head is in the raised position dressing the abrasive as required between polishing operations; means advancing said polishing head toward and engaging said abrasive end portion with a workpiece while said polishing head is in the lowered position; a driven gear drivingly connected to said spindle; and power means drivingly engaging said gear rotating said abrasive member polishing the workpiece aperture edges while said abrasive is advanced against the workpiece.
 3. An apparatus for polishing spArk plug aperture edges in curved rotary engine housings, the apparatus including: a frame; a rotating polishing head movable vertically between a lowered polishing position and a raised abrasive feeding and dressing position; said polishing head also being movable horizontally when in the lowered polishing position for advancement into engagement with a surface of the curved rotary engine housing at the point it is intersected by the spark plug aperutre; said polishing head comprising a housing; a cylindrical spindle; a bearing assembly adjacent each end of said spindle rotatably supporting it within said housing; a collet positioned within said spindle; a cylindrical abrasive member adjustably retained within said collet with an end portion extending outwardly from a forward end of said collet and said spindle for polishing the rotary engine housing; a tapered surface on the internal periphery of said spindle adjacent said abrasive member end portion; a tapered surface on the exterior of said collet adjacent said abrasive member end portion; an abutment on the rearward end of said collet; a spring between said abutment and the rearward end of said spindle biasing the tapered surface on said collet into engagement with the tapered surface of said spindle squeezing said collet against said abrasive member retaining it in a position with said end portion extended; the biasing force of said spring also being sufficient to frictionally engage said collet and said spindle tapered surfaces providing a driving connection therebetween rotating said collet with said spindle; first actuating means selectively engageable with said abutment moving said collet against the force of said spring and disengaging said tapered surfaces releasing said collet from said abrasive member; second actuating means selectively engageable with said abrasive member and movable a predetermined distance for extending said end portion out of said collet a predetermined working distance; a dresser unit mounted on said frame; means actuating said dresser unit moving it into engagement with said end portion of said abrasive member while the polishing head is in the raised position dressing the working end of said abrasive member as required between polishing operations; third actuating means advancing said polishing head toward and engaging said abrasive member end portion with said engine housing spark plug aperture while said polishing head is in the lowered polishing position; a driven gear drivingly connected to said spindle; and power means drivingly engaging said gear rotating said abrasive member polishing the spark plug aperture edges while said abrasive is engaged with the rotary engine housing. 